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Extreme weather linked to climate change: study

TONY EASTLEY: One month after the floods and cyclone that battered Queensland and a day after a record downpour in Darwin comes research claiming to prove a link between intensifying extreme rain events and man-made greenhouse gas emissions.

The authors of the paper published in Nature today say extreme rains and floods increased by 7 per cent in the second half of last century right across the Northern Hemisphere.

AM's David Mark reports.

DAVID MARK: It seems whenever there's heavy rain, a flood or a cyclone, the question is asked:

ROGER STONE: To what extent has that been nudged, or as I like to say aggravated by a little bit of climate change going on as well?

DAVID MARK: That's Roger Stone, a professor in climatology and water resources at the University of Southern Queensland.

And it's a fundamental question. Up to now the answer has been based purely on theory.

But in an article for Nature two Canadian scientists say they've proved a link between heavy rainfall events and man-made climate change - at least in the northern hemisphere.

Dr Francis Zwiers from the University of Victoria is one of the authors.

FRANCIS ZWIERS: We saw that there was a pattern of change that is simulated by the climate models that is detectable in observation. So that suggests that humans influence the intensity of precipitation extremes.

ROGER STONE: In other words strong storms and heavy storms that can dump a lot of rainfall in a very short period of time, that can cause as we've seen I guess in the last few months flash flooding and a lot of very intense localised flooding which can do enormous damage.

DAVID MARK: The two Canadians found that those heavy rainfall events have increased by 7 per cent over the past 50 years.

They make the connection with climate change by looking at rainfall totals collected between 1951 and 1999 from 6,000 rain gauges across the northern hemisphere.

They then ran complicated computer models with climate change factored in which correlated with the rainfall pattern they observed.

FRANCIS ZWIERS: Well it has often been suggested that the changes in precipitation extremes are likely linked to greenhouse gas increases.

Prior to this time there had not been a study that had formally identified this human effect in precipitation extremes. And so this paper provides specific scientific evidence that that is indeed the case.

DAVID MARK: Professor Roger Stone says it can be extrapolated that if climate change is causing more heavy rainfall in the northern hemisphere it's also happening in Australia.

ROGER STONE: The CSIRO models have already demonstrated that to I think a good extent, certainly for a region just such as south-east Queensland that we do get increased, enhanced what's called deep convection under a climate change scenario.

DAVID MARK: Professor Stone you're an expert in this field. Are you satisfied that the science in this particular paper is robust; that there is a cause and effect link between those increased greenhouse gas emissions and those increased rainfall events?

ROGER STONE: Well I think definitely it's a robust study. It's part of the scientific discovery that we're going through with this interesting area of research.

And the fact that it's published in one of the world's most prestigious journals, which is Nature, I think speaks for itself.

TONY EASTLEY: Professor Roger Stone from the University of Southern Queensland ending David Mark's reports.

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